text: By . Sarah Griffiths . PUBLISHED: . 12:40 EST, 23 January 2014 . | . UPDATED: . 12:40 EST, 23 January 2014 . A plant virus has been found in honeybees and could help explain their decline. U.S. and Chinese scientists have found the tobacco ringspot pathogen, which attacks tobacco plants and soybeans, is increasingly prevalent in declining honeybee colonies. They say it is the first evidence that honeybees exposed to infected pollen can become infected too. U.S. and Chinese scientists have found the tobacco ringspot pathogen, which attacks tobacco plants and soybeans, is increasingly prevalent in declining honeybee colonies (pictured) The use of pesticides, loss of habitat and climate change has previously been blamed for the shrinking of honeybee populations. ‘The results of our study provide the first evidence that honeybees exposed to virus-contaminated pollen can also be infected and that the infection becomes widespread in their bodies,’ the study's lead author, Ji Lian Li of the Chinese Academy of Agricultural Science, said. The virus was also found in varroa mites – a beehive pest described as a ‘vampire parasite’ that is also believed to weaken colonies by transmitting disease while feeding on their blood. The researchers made their discovery after screening bees for frequent and rare viruses. Tobacco Ringspot Virus (illustrated) is not the only virus now known to attack honeybee colonies but it is the first evidence that honeybees exposed to infected pollen can become infected too . Around five per cent of known plant viruses are pollen-transmitted and are therefore potential sources of host-jumping viruses, they explained in their paper, which was published in the journal mBio. These viruses tend to be particularly dangerous because they lack a genetic function that edits out errors in replicated genomes so that they can generate a flood of variant copies with different infective properties. High replication rates mean viruses appear to work together to determine the suffering of their hosts. ‘The viruses are a likely source of emerging and re-emerging infectious diseases,’ the researchers said. The virus was also found in Varroa mites - a beehive pest described as a 'vampire parasite' that is also believed to weaken colonies by transmitting disease while feeding on their blood. This mite has been magnified many times and is clinging to hairs on a bees's leg . Tobacco Ringspot Virus (TRSV) is not the only virus now known to attack honeybee colonies. When the researchers investigated bee colonies classified as strong or weak, TRSV and other viruses were more common in the weak colonies than they were in the strong ones. They said that bee populations with high levels of multiple viral infections began failing in late autumn and perished before February. In contrast, those in colonies with fewer viral assaults survived the entire cold winter months. ‘The increasing prevalence of TRSV in conjunction with other bee viruses is associated with a gradual decline of host populations and supports the view that viral infections have a significant negative impact on colony survival,’ the researchers said. Honeybee populations are declining sharply . There are only enough honeybees in Britain to properly pollinate a quarter of the country’s crops, scientists claim. Destruction of huge swathes of grassland and the use of agricultural chemicals have caused a spiralling drop in the populations of honeybees, which are vital for food production. Professor Simon Potts of the University of Reading, who led the research project, said: ‘We face a catastrophe in future years unless we act now.’ The research, published in the journal PLOS One, found that Europe has 13.4million too few honeybee colonies to properly pollinate all its crops. Bee populations have plummeted as their meadowland habitats were concreted over and their wildflower food supply killed by herbicides. Previous studies have estimated that the number of British honeybees have halved over the last 25 years. Scientists think the bee shortfall is leading to reduced crop yields and they warn that in future farmers may have to look at mechanical or hand pollination.